So-called polymer alloys are known as plastic molding materials and are prepared by blending two or more kinds of resin materials by kneading or by other means so as to allow each resin material to compensate for disadvantages of the other resin materials.
Known as one of such polymer alloys is a resin composition comprising 100 parts by weight of a polyarylate and 100 parts by weight or less of a polyamide, and which is excellent in all of heat distortion resistance, molding properties and chemical resistance (refer to JP-B-56-14699 and JP-A-52-98765). (The terms "JP-B" and "JP-A" as used herein mean an "examined Japanese patent publication" and an "unexamined published Japanese patent application", respectively.)
According to the above prior art references, not only the molding properties but also the chemical and oil resistances of a polyarylate are improved by blending it with a polyamide. On the other hand, it is expected that a resin composition having well-balanced properties can be obtained by dispersing a polyarylate into a polyamide to take advantage of the good molding properties and chemical resistance of the polyamide and to impart to the composition the good heat distortion resistance of the polyarylate. However, it is generally difficult to uniformly and finely disperse a polyarylate into a polyamide. In the case where the dispersion of the polyarylate is not uniform and the dispersed polyarylate particles are coarse, well-balanced properties cannot be obtained and the resin composition has problems such as, for example, poor molding properties, poor chemical resistance and low strengths. Although it is essential to uniformly and finely disperse a polyarylate into a polyamide for making the composition exhibit excellent properties, there has not yet been found a method effective in attaining the desired dispersion.
On the other hand, although the polyarylatepolyamide composition has both excellent heat distortion resistance attributable to the polyarylate and excellent molding properties and chemical resistance attributable to the polyamide, such properties alone are insufficient in some applications. Since the above resin composition has a disadvantage of being poor in impact resistance, specifically in both Izod impact strength and high-speed punching impact strength, the resin composition has limited application.
As compositions free from the above drawback, there have recently been proposed resin compositions prepared by incorporating various modified polyolefins as an impact resistance improver into the above-described resin composition (see JP-B-62-944, JP-A-61-183353 and JP-A-62-277462).
These resin compositions containing the above-mentioned impact resistance improvers are to some extent improved in that molded articles obtained therefrom have high Izod impact strengths as compared with molded articles obtained from resin compositions not containing the above-mentioned impact resistance improvers. However, the above-proposed resin compositions are still insufficient in high-speed punching impact strength, which is important from a practical standpoint. The high-speed punching impact strengths of these resin compositions are very low particularly at low temperatures of around -30.degree. C. and, hence, problems will be caused if such resin compositions are used for the production of exterior automobile trim parts which are required to have such low-temperature high-speed impact resistance.
Further, the use of modified polyolefins as an impact resistance improver has the problems that there are cases where molded articles develop surface defects such as silver streaks and flow marks and that the modified polyolefins impair the weld strength of molded articles.
The present inventors have conducted intensive studies to overcome the problems described above. As a result, they have succeeded in developing a thermoplastic resin composition having good impact resistance while retaining the excellent physical properties.